Respiration moves oxygen across lung membranes into the bloodstream and, in reverse, flushes carbon dioxide from the body. Inhaled particles, drugs, inflammatory molecules, and even cancer cells traverse these delicate barriers. In an effort to mimic what occurs naturally, scientists at Harvard’s Wyss Institute for Biologically Inspired Engineering have created an artificial lung-on-a-chip by layering cells that line human lung airsacs and blood vessels on a porous, flexible membrane. This translucent device, roughly the size of a rubber eraser, induces the membrane and cells to expand and contract under vacuum pressure to imitate breathing; air flows on one side of the membrane, while fluid containing human immune cells flows on the other. The miniature lung mimics the way tissue absorbs nanoparticles and bacteria—and the resulting immune responses or toxic reactions, says Donald Ingber, founding director of the Wyss Institute and the project’s leader. The device could reduce reliance on animals as research subjects, Ingber says, and cut the time and costs involved in bringing new drugs to market.